This invention relates to the manufacture of alkanesulfonic acids and alkanesulfonyl chlorides by oxidation of the corresponding alkanethiol, dialkyldisulfide or alkyl alkanethiolsulfonate. More particularly, it relates to the oxidation of such corresponding compounds in mixtures of hydrogen peroxide and hydrogen chloride to form alkanesulfonic acids and alkanesulfonyl chloride free of undesirable side products arising from side-chain chlorination of the alkyl group as commonly observed in direct chlorine oxidation.